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It may seem obvious, but science has confirmed that daylight saving time disrupts our body clock, especially if we're late risers.

Dr. Till Roenneberg of Ludwig-Maximilians University in Munich, Germany, and colleagues report their findings in the journal Current Biology.

"Our data indicate that the human circadian system does not adjust to DST [daylight saving time]," the researchers say.

A quarter of the world's population is subjected to a one-hour time change twice a year, yet the impact of this change is poorly understood by science.

Circadian clocks use daylight to synchronize the body to the environment and regulate sleep.

Roennenberg and team set out to study the impact of daylight saving time on the sleep patterns of 55,000 people in Central Europe.

'Until now most of the impact of daylight saving time has been anecdotal. One of science's aims is to find evidence for things that seem common sense.'—Dr. Greg Roach, sleep expert

They found that during standard time, people tended to adjust their wake up time to fit in with the dawn, but this adjustment did not happen during daylight saving time.

Larks vs. owls

In a separate study, Roenneberg and team looked at 50 people whose natural inclination was to wake up early ("larks") or late ("owls"). The researchers found that both larks and owls adjusted well to the release from daylight saving time in autumn, but had problems adjusting to the imposition of daylight saving time in spring.

This was particularly the case for the late rising owls.

Roennenberg and team say the effects held for weeks, perhaps causing people to feel continually sleep-deprived in the spring and summer.

Australian body clock researcher Dr. Greg Roach of the University of South Australia's Centre for Sleep Research says the study is commendable, even if it does confirm what many of us already know.

"It's the best study I've seen linking sleep patterns with daylight saving time," he says.

"Until now most of the impact of daylight saving time has been anecdotal," says Roach. "One of science's aims is to find evidence for things that seem common sense."

Roach says the human body clock tends to run a bit longer than 24 hours, which means that people would naturally wake up a bit later every day if removed from the influence of changing day lengths.

This explains why late risers would find it harder to adjust when the clock moves forward, robbing them of an hour of sleep, he says.

But Roach thinks the survey findings that show people adjust their wake up time to fit in with the changing time of dawn would not generally apply to people who live in cities.

"In cities, the time that determines what time you get up is what time you need to get the kids to school or what time you need to be at work," he says.

In Canada,Daylight Saving Time used to runfrom the first Sunday in April until the last Sunday in October.

Starting this year,it began on the second Sunday in March and ends on the first Sunday in November - Nov. 4.

It's up to each province to decide whether to use daylight time. Most of Saskatchewan has not observed daylight time since 1966 and stays on Central Standard Time all year round.

Some border towns follow the time schemes of their neighbours in Manitoba or Alberta.Areas of Quebec east of 63 degrees west longitude do not change to daylight time and remain on Atlantic Standard Time year round. Pockets of Ontario and British Columbia do not use daylight time.